Numerous methods of contraception are available today, including oral contraceptives, intra-uterine devices (IUDs), sterilization and vaginal spermicides. When taken according to directions, oral contraceptives provide protection which is nearly 100 percent effective. IUDs are almost equally effective and particularly appropriate for parous women. Sterilization is effective and has few apparent adverse effects for couples who want essentially permanent protection. Vaginal spermicides have been shown to be generally effective. If they are used correctly, spermicides can be more than 95 percent effective; even if not used correctly all the time, spermicides are apparently about 85 percent effective. A 1976 study of U.S. women using contraception showed that about 15 percent of spermicide users became pregnant within the first 12 months of spermicide use. In contrast, 2 percent of pill users and about 4 percent of IUD users became pregnant within the first 12 months of use. Barrier Methods, Population Reports, Series H, No. 5, H77-78. (1979).
Each of the available methods of contraception has disadvantages which must be considered in assessing their appropriateness for and acceptability to users. For oral contraceptives, important disadvantages are the need to take the pill on an ongoing basis and the numerous reports of adverse reactions associated with their use. IUDs have several problems associated with their use, including incorrect placement, dislodging after insertion, bleeding and pain. Sterilization requires a surgical procedure and one of its biggest advantages--its permanence--may prove to be a major disadvantage if decisions about childbearing are reversed. The major disadvantages of spermicidal contraceptives are that they must be used close to the time of intercourse; require a relatively long waiting period before they are effective; provide protection of relatively short duration; generally require re-application before each act of intercourse; and may leave a messy residue. These disadvantages, in addition to improper placement of the contraceptive in the vagina, are important causes of the failure of spermicides to provide protection as effective as that available from other methods.
Despite these disadvantages, vaginal spermicides do have distinct contraceptive advantages. For example, they are readily available as nonprescription formulations; can be used on an "as needed" basis; and produce few adverse physiological effects. As a result, they have considerable promise as an alternative to other available contraceptive methods.
There are at least seven different forms of vaginal spermicidal products available today: creams, jellies, foams, effervescent tablets, biodegradable soluble films, sponges and suppositories. Vaginal spermicide formulations consist of the spermicide dissolved in or mixed with an inert base. The inert base serves to carry the spermicide and hold it in the vagina; it may also act as a barrier which interferes with direct contact between the sperm and cervical mucous. The spermicide is a chemically active ingredient which incapacitates the sperm.
There have been countless attempts to provide effective protection through the use of vaginal spermicides, as evidenced by the extensive literature and the number of patented formulations and commercially available products. For example, two types of foam are available: foams supplied in pressurized cans and foaming tablets or suppositories. Both types have the disadvantages enumerated: application is necessary prior to intercourse; only short-term protection is provided; re-application is necessary, etc. Foaming tablets require large amounts of moisture in the vagina and may take as long as 20 minutes to ensure foaming action. Some suppositories also require large quantities of vaginal fluid and, because they have melting points higher than the vaginal temperature, do not consistently release all of the active ingredient.
There have been attempts to solve some of the problems associated with vaginal spermicides. Kazmiroski et al (U.S. Pat. No. 4,384,003) disclose a vaginal contraceptive suppository which is said to have both rapid release of an active ingredient and prolonged effectiveness. The suppository disclosed is comprised of a mixture of sodium starch glycolate, a thickening agent, and a vegetable oil base combined with a spermicide. The resulting composition is said to release the active ingredient in less than 15 minutes and maintain effectiveness for up to 6 hours. The extended duration of spermicidal action which is apparently due to the production of a thick, non-runny paste which will not leak from the vaginal orifice.
Laughlin et al. (U.S. Pat. No. 4,031,202) disclose a controlled release article which is claimed to provide substantially immediate release of a material releasably affixed on the outside of the article and subsequent release of compounds contained within the article. The immediate release agent can be a spermicide and is affixed on the outer surface of a container which releasably encloses a solution of a micelle-forming compound. The compound is said to be able to migrate through a microporous membrane and provide an effective spermicide concentration over a 21-day period. The article is said to provide contraceptive protection when allowed to remain in the vagina between menstrual periods.
Contraceptive films, which are water soluble films, have been developed for use as vaginal spermicides. The effectiveness of these C-films, as they are called, is unclear. Studies with a flat sheet of this dissolving film showed pregnancy rates of 9 to 62 per 100 woman-years. Barrier Methods, Population Reports, Series H, No. 5, H103 (1979). Such contraceptive film is being modified for easy, effective use by the male partner. Fast-dissolving films used in making these water-soluble or spermicidal condoms are said to release the active agent quickly and thus provide rapid spermicidal action. There is, however, no long-term protection and a new film must be used each time intercourse occurs.
Long-term spermicide release can be achieved through the use of nondissolving delivery systems, such as vaginal rings or cervical caps which release spermicides. Neither of these configurations provides for immediate or at least quick release of spermicide.
Drobish et al. (U.S. Pat. No. 4,304,226) disclose a cervical cap to be used to deliver spermicide in the vagina. The cap is claimed to be designed to remain in the vagina between menstrual periods, during which time it is to provide release of the spermicide.
Although much effort has been expended toward developing a vaginal spermicide which is acceptable to the user and effective in providing contraceptive protection, there is at present no vaginal spermicide which does not suffer from one or more of the aforementioned disadvantages. Currently available formulations which are used on an "as needed" basis require a relatively long time after insertion before they provide effective spermicide concentrations, provide only short-term protection and leave a messy residue. Spermicides which are delivered continuously over a period of several days or weeks (e.g., from a vaginal ring or cervical cap) provide no immediate protection and are released during times when no protection is necessary, thus unnecessarily exposing the user to the long-term side effects of spermicides.
What is needed, therefore, is a means of providing an immediate release of effective concentrations of spermicide upon placement in the vagina and a prolonged release of the spermicide. This dual approach is necessary to provide protection against the first ejaculate, thus eliminating the need for a waiting period between insertion and intercourse, and further protection for an extended period, thus eliminating the need for re-application before each act of intercourse (as well as for insertion immediately prior to intercourse). Although there are formulations presently available for use on an "as needed" basis, none provides this highly desirable combination of quick release of effective spermicide concentrations followed by prolonged spermicide release which provides contraceptive protection.